If your income was too high to deduct an IRA contribution, or you have heard people talk about a backdoor Roth IRA, there is a small tax form that ties it all together. Its whole job is to make sure the money you already paid tax on does not get hit a second time when you take it out.
A lot of people skip it, often without realizing they were supposed to file it, and that quiet mistake can cost real money years later. This guide explains what IRS Form 8606 is, who needs to file it, how it works for a backdoor Roth, how to fill it out, and how to fix things if you missed it in the past.
Form 8606 is the IRS form titled Nondeductible IRAs. In short, it reports the after-tax money moving in and out of your retirement accounts. The Internal Revenue Service uses it to keep a running record of your basis, which is the total of all the non-deductible contributions you have ever made to an IRA.
There are four situations where this form comes into play. You file Form 8606 to report a non-deductible contribution to a traditional IRA, a conversion of a traditional, SEP, or SIMPLE IRA to a Roth, a distribution from an IRA that holds basis, or certain Roth IRA payouts. It is one of the IRS forms that gets attached to your Form 1040, the same federal tax return you file each year.
Think of it as a receipt you keep for life. Every dollar you already reported gets logged here, so the IRS knows not to charge you again later.
The reason it exists comes down to fairness. When you contribute to a traditional IRA and cannot deduct it, you have already paid income tax on that money. Years later, when you pull it out or convert it, the IRS has no way of knowing part of it was basis unless you told them. Without the form, the IRS assumes every dollar coming out is fully taxable.
That is how people end up paying tax twice on the same money. Form 8606 helps you avoid that double taxation by proving how much of your IRA you already taxed, which ensures the IRS treats that portion correctly when it leaves the account.
Skip it, and you can hand the government unnecessary taxes on money that should have stayed yours. That is a costly trade for a form most people can finish in one sitting.
You are required to file Form 8606 in any year one of these things happens. You made nondeductible contributions to a traditional IRA. You converted it into a Roth. You took a distribution from an IRA while you still had basis sitting in it. Or you took certain Roth withdrawals. In plain terms, you must file Form 8606 if you made after-tax contributions or moved money in a way that touches your basis. If you have not filed Form 8606 in past years, those gaps are worth a look.
A couple of details trip people up. If both you and your spouse made non-deductible IRA contributions, each of you files a separate form, since the basis is tracked per person. And even if your income is low enough that you do not have to file a return at all, you still need to file the standalone form by the normal deadline when one of those events applies.
When in doubt, it is safer to complete Form 8606 when required than to assume it does not apply. The cost of filing is a few minutes. The cost of skipping it can follow you for years.
For higher earners, the form shows up most often because of the backdoor Roth IRA. It is a popular Roth IRA strategy for people whose income is too high to contribute to a Roth directly.
The move itself is simple. You make a non-deductible contribution to a traditional IRA, then move that money from the traditional IRA to a Roth IRA soon after. Because you already paid tax on the contribution, this Roth conversion is usually tax-free. On the form, you report the contribution in Part I of Form 8606 and the conversion in Part II. You'll need to file the form for the year the contribution applies and again for the year you convert.
There is one rule that catches people. The pro-rata rule says the IRS looks at all your traditional IRAs together when you convert an IRA to Roth, including any SEP IRA or SIMPLE accounts. If you have other pre-tax money sitting in any of them, your conversion is not fully free of tax. Instead, the taxable and nontaxable parts are blended based on your total IRA balance on December 31. So a clean backdoor Roth usually means having no other pre-tax money in your IRA mix.
Filling it out is less scary than it looks once you know the form is split into three parts. Part I handles your nondeductible contributions to traditional IRAs and any distributions from a traditional IRA, including the traditional IRA contributions and certain contributions you could not deduct. Part II covers conversions to a Roth, and Part III is only for Roth distributions.
You only complete the form parts that match what you did during the year, so a straightforward backdoor Roth usually means Part I and Part II and nothing else. Keep your year-end IRA statements handy, and use Form 5498, the contribution summary your IRA custodian sends to you and the IRS, to confirm what went in. One detail to watch when it is time to file your taxes is the year: a contribution you made in early 2025 for tax year 2024 belongs on the 2024 form, not the 2025 one.
If the math around basis and the pro-rata rule starts to feel heavy, that is normal. This is the point where many people hand it to a tax preparer rather than risk an error that shows up years later.
Plenty of people discover an old backdoor Roth or a string of non-deductible contributions that never made it onto a return. The good news is a missing Form 8606 is fixable.
You can file a prior-year form on its own, even years later, because it can stand alone and you do not always have to redo the whole return. If other parts of that year also need changing, you would file an amended return on Form 1040-X and attach a corrected Form 8606. Either way, you are rebuilding the basis record that protects you from overpaying. It also helps to check whether you already included Form 8606 in any past year before you refile, so you do not report your non-deductible amounts twice.
There are two penalties to know about. The IRS may charge a $50 penalty for each year you were required to file and did not, and a $100 penalty for overstating nondeductible contributions. Both can be waived if you show reasonable cause, which is why a short explanation often goes a long way. Sorting out a late form on your own terms helps you sidestep unnecessary taxes and penalties in the future, and it beats waiting for the IRS to notice the gap.
The 8606 has a way of piling up quietly. A client does backdoor Roths for five years, never files the form, and then it lands on a CPA firm's desk as a basis reconstruction project right in the middle of tax season. Multiply that by a few clients and it eats real hours.
This is the kind of detailed, records-heavy prep Madras Accountancy handles for U.S. CPA firms. We rebuild basis from old statements and Form 5498s, prepare current and prior-year forms, and keep the tracking clean so the same scramble does not repeat next year. If these cleanups are stealing your team's tax filing time, it is worth a conversation.
What is Form 8606 used for? Form 8606 is used to report non-deductible IRA contributions, conversions to a Roth, and withdrawals from IRAs that hold after-tax money. It tracks your basis so the IRS does not charge the same dollars twice. You file it with your return.
Do I have to file for a backdoor Roth? Yes. A backdoor Roth IRA has two reportable steps, the non-deductible contribution and the conversion, and both go on the form. You report the contribution in Part I and the conversion in Part II. Each spouse who does one files separately.
What happens if I never filed it? You can fix it by filing the missing form for each prior year, sometimes with an amended tax return. This rebuilds your basis so you are not charged again later. A $50 penalty can apply per year, but reasonable cause often clears it.
What is the penalty for not filing Form 8606? There is a $50 penalty for failing to file when required, and a $100 penalty for overstating your IRA basis. Both can be excused if you show reasonable cause, so it is usually worth filing the late form rather than leaving the gap.
Does the form get filed with my tax return? Usually yes. It is attached to your return and filed by your normal deadline. If your income is low enough that you do not need to file a federal income tax return, you still must file IRS Form 8606 as a signed standalone form by the same date.
What is the pro-rata rule? The pro-rata rule means the IRS treats all your traditional IRAs, including SIMPLE IRAs, as one pool when you convert. If you hold pre-tax money in any of them, part of your conversion becomes taxable, based on the money in your IRA on December 31.
Do my spouse and I each need one? Yes, if you both made non-deductible contributions or did backdoor Roths. Basis is tracked per person, so each spouse files their own form. A married couple doing backdoor Roths together should end up with two forms on the same return.
Should I keep old 8606 forms? Definitely. Your 8606 is a lifetime record of your IRA basis, so keep every year's copy with your records. When you eventually take a distribution or do a conversion, those past forms prove how much was already paid.
It looks like a small form, and most years it is. The trick is remembering to file it every time you make a nondeductible contribution or move money into a Roth, because the basis it tracks is what keeps your own money from being charged twice. If you are sitting on years of backdoor Roths and are not sure your filings are clean, a quick review with someone who handles these often can save you a real headache. Madras Accountancy is glad to help your firm sort it out.
This article is general information, not tax advice. IRA and tax rules change and depend on your situation, so check with a qualified tax professional about your own facts.
Single-entry vs double-entry bookkeeping made simple: how each accounting system works, the key differences, and which one your small business needs.
%2075-100%20(12).png)
CPA vs EA (enrolled agent) vs tax attorney: how each tax professional differs, who can represent you to the IRS, and which fits your tax needs.
%2075-100%20(9).png)
Learn how tax professionals should respond to a data breach, report theft to the IRS and states, notify clients, meet FTC rules, and prevent future attacks.
